1. Field of the Invention
The present invention generally relates to devices for monitoring the heart and surrounding blood vessels, and more particularly to such a device which provides improved signal conditioning.
2. Description of the Prior Art
Every year, more than 550,000 people die of heart attacks in the United States alone. In fact, heart disease is the number one killer of persons living in the U.S. Heart attacks are usually brought on by the accumulation of fat and other substances within the coronary arteries, those vessels which supply the heart itself with oxygen and nutrient-rich blood.
Research scientists are getting closer to the secret of preventing heart attacks. The most important aspect of prevention is detecting the presence of arteriosclerosis before it advances to a critical stage. There are many instruments currently in use for invasive and noninvasive measurement of various cardiac parameters. Techniques include ballistocardiography, electrical impedance measurements, ultrasonics, and vibrocardiography. The present invention is more related to traditional cardiac monitoring using electrocardiograms (ECG) and phonocardiograms (PCG).
The ECG signals resulting from the electrical activity of the cardiac muscle are extremely valuable diagnostic indicators when viewed by an experienced cardiologist. Certain abnormalities in these signals can be indicative of different types of heart disorders. Similarly, acoustic patterns taken via PCG may also provide useful information. The difficulty in recording this data, however, lies in the fact that stray electrical potentials can distort the measurements and obscure useful information hidden in the instrumentation output. Signals in analog form are often recorded on magnetic tape, then reproduced at a later time for conversion to digital form for processing. When the connection is made between the recorder output and the processing equipment, powerline noise can be introduced, in addition to circulating electric currents in ground loops.
Another problem arises in placement of the electrodes or transducers on the human body. Any such devices should have a high degree of isolation from the AC powerline and from the powerline ground for safety reasons. Commercially available magnetic tape recorders do not have the required input circuit isolation. Thus, the recorders cannot be connected directly to the electrodes or transducers, creating further potential for signal loss.
Finally, even if the signals could be recorded without distortion, it has been found that certain low-frequency components of the acoustic signal having a relatively large amplitude tend to drown out the higher-frequency components. Much vital diagnostic information is thereby lost.
It would, therefore, be desirable and advantageous to devise a system for monitoring the ECG and PCG of the heart whereby excessive external noise is minimized. The system should allow for connection of the recorder to the electrodes and transducers without introducing ground loop currents, and should also provide a means of preserving high-frequency acoustic signals for later processing.